The decoding circuit of the present invention relates to devices concerned with providing an audiophile with a more realistic and true-to-life rendition of a recorded performance. The concept of stereophonic high fidelity recording was the first step forward in trying to give a listener a more realistic feeling of being present at a live performance. This was done by providing two separate channels of sound played back through separate speakers. Recently there have been new developments in quadraphonic sound, some of which have included the use of four separate channels of sound while others have utilized synthetic additional channels. The purpose of the additional channels was to obtain the ambience of a performance by utilizing the background noise that would normally be present in an orchestra hall, for example. A drawback with such systems is that they require that the listener purchase new equipment capable of handling four channels of sound.
Conventional decoding circuits are of two basic types: active and passive. The active type decodes the sound at low levels, i.e., before amplification, necessitating duplicate additional amplifiers and the accompanying controls; thus the requirement for new equipment to replace existing stereophonic equipment where such active devices are utilized. In addition to requiring an expensive replacement to obtain the quadraphonic sound, the additional complexity adds to the probability of component malfunction. Previous passive type decoders which can be used with existing equipment simply couple two additional speakers in series across the speaker terminals of a stereo amplifier, occasionally utilizing a resistance to give some separation. Effectively this is an arithmetic addition. It takes no account of the phase relationship between the channels permitting the additional speakers unfavorably to interact with one another, producing fuzzy sound which is directionally ambiguous and fatiguing.
The present invention utilizes a simple passive design which takes advantage of natural acoustic principles to overcome the above deficiencies of previous passive decoding circuits.
It is accordingly an object of the present invention to provide a circuit for cross-coupling the signals of a conventional stereophonic amplifier to produce additional channels therefrom for driving additional loud speakers placed in a listening area.
It is another object of the present invention to produce a decoding circuit which can reproduce signal differences between the left and right channels of a stereo amplifier with selected polarity and phase relationship.
It is another object of the present invention to provide a decoding circuit which can be added to a stereophonic amplifier for providing four distinct channels of sound.
Other objects and advantages of the invention will appear more fully in the concluding portion of this specification.